The ever decreasing size of electronic components, such as integrated circuits, and the associated reduction in center line spacings of contacts of the components and of the circuits on which they are mounted raises substantial difficulties in the manufacture of connectors. It does because the traditional tolerances in metal and plastic parts for connectors, expressed in several thousandths of an inch, are now being achieved in the components and circuits themselves in terms of conductive path widths and spacings.
Because of this, a number of approaches have been taken which employ very small conductive particles held in a matrix of insulating material including adhesives. These materials are variously whisker-like particles, or slivers, or platelets and flakes which are either fabricated of precious metals or of inert ingredients coated with precious metals. These various elements can range in size from ten to twenty microns in width or diameter up to 25 or 30 microns in maximum dimension. The elements are held in various binders, including pressure sensitive or hot melt and polymerizable adhesives and in elastomeric materials. The resulting product may be termed to be a conductive elastomer or a conductive adhesive, and both operate to interconnect the conductive paths of components to the conductive paths of circuits when such elements are forced together against the conductive element. The forcing together forces the conductive particles to touch each other and to contact the paths being interconnected to form electrical interconnections. U.S. Pat. No. 4,729,809, granted Mar. 8, 1988, is drawn to anisotropically conductive adhesive composition and details a conductive adhesive composition which is, in essence conductive in one direction. It mentions that the conductive particles have a tendency to form clusters during the mixing of the composition and also that larger particles may be employed, which are of a sufficient size to provide single particles conduction through an adhesive layer which is on the order in thickness of the diameter of the particles.
The foregoing patent and numerous other patents and teachings relating to conductive elastomers and/or adhesives employ a random placement of conductive particles in an insulating medium and depend upon the mixture of the composition to result in their being at least sufficient particles to form an interconnection when the composition is compressed between conductive paths. This randomness causes no particular problems when the areas of the conductive paths to be joined are relatively large compared to the size and number of particles and the spacing thereof, making the provision of particles statistically such as to assure interconnection.
But as the dimensions between conductive paths to be interconnected shrink, the statistically based random disposition of particles can become less reliable. Moreover, the randomness almost assures discrepancies as between contact paths manifest in variations in conductivity or resistivity and occasionally, variations in capacitive and inductive effects of the differently dimensioned conductive pathways based on the orientation, number, and disposition of not only the conductive particles, but of the insulating medium and thus the dielectric values of the interconnection.
Another problem facing the foregoing connection devices and techniques relates to the dependence upon the characteristics of adhesion which are directly related to the chemistry of the adhesive, its mixture and handling, shelf life, and relative volatilization.
Accordingly, the present invention has as an object the provision of an electrical connector and a method of manufacture which features an ordered disposition of fine conductive particles in a preformed sheet of insulating and dielectric material to provide an array of discrete contact elements, each essentially identical to the other in electrical and mechanical characteristics. The invention has as a further object the provision of a sheet of thin insulating material containing fine conductive particles forming an area array connector for interconnecting contact paths on very close centers and with very small spacing of paths between components and circuits. Still a further object is to provide a method of manufacturing ordered electrical connectors having discrete contacts on very fine centers. The invention further contemplates an objective of providing a thin film-like ordered array of conductive particles wherein the particles and the insulating matrix can be preformed and assembled together utilizing adhesive substances for mechanical purposes.